<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>原型和 in 操作符</title>
</head>
<body>
  <script>
    let k1 = Symbol('k1'),
      k2 = Symbol('k2');

    let o = {
      [k1]: 'k1',
      [k2]: 'k2',
      c: 3
    };

    console.log(Object.getOwnPropertySymbols(o));  // [Symbol(k1), Symbol(k2)]
  </script>
</body>
</html>